These devices, associated with an electronic control system, are known particularly for providing the automatic control of the butterfly valve of a carburetor or of an equivalent control element such as the fuel injection pump lever for diesel cycle vehicles, while preserving the usual mechanical control from the accelerator pedal, so as to make it possible, on the one hand, for the driver to permit the automatic control of the speed of the vehicle, for example by a system of imposed speed (VI) observing the speed limits, while preserving at any moment the possibility of manually accelerating the engine to pass in overspeed for example and, on the other hand, to provide the idling speed control of the internal combustion engine of the vehicle. These known devices prove relatively bulky and expensive to make and to use, at the level of the reduction gear and especially of the electric contact switch which plays an essential role, by indicating to the control system, when it is functioning as a speed or idling regulator, whether the control element is placed under the direct control of the driver or not.